[PATCH net v3 5/6] amt: make pre-query report drops visible

[Omar Ramadan]

A gateway cannot forward an IGMP or MLD report until it has received the
relay's Membership Query for that family.  The Query supplies the
response MAC the Update echoes, so dropping an early report is required,
but doing so silently leaves operators with a dark multicast path and no
indication why the join never happened.

Emit a family-specific debug message before taking the existing drop
path.  That path already increments tx_dropped, so each discarded report
is accounted exactly once.

Assisted-by: LLM
Signed-off-by: Omar Ramadan <omar@xxxxxxxxxxxxx>
---
 drivers/net/amt.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/net/amt.c b/drivers/net/amt.c
index 2feb418..fec3265 100644
--- a/drivers/net/amt.c
+++ b/drivers/net/amt.c
@@ -1249,9 +1249,17 @@ static netdev_tx_t amt_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 		/* Gateway only passes IGMP/MLD packets */
 		if (!report)
 			goto free;
+		/* A validated report can only be forwarded after the relay's
+		 * family-specific Membership Query supplies the state echoed
+		 * by the Membership Update. Log this readiness failure before
+		 * the shared drop path accounts it.
+		 */
 		if ((!v6 && !READ_ONCE(amt->ready4)) ||
-		    (v6 && !READ_ONCE(amt->ready6)))
+		    (v6 && !READ_ONCE(amt->ready6))) {
+			netdev_dbg(dev, "drop %s report: no Membership Query for this family yet\n",
+				   v6 ? "MLD" : "IGMP");
 			goto free;
+		}
 		if (amt_send_membership_update(amt, skb,  v6))
 			goto free;
 		goto unlock;
-- 
2.43.0